1. Field of the Invention
This invention relates to photography. More particularly, it relates to photographic film containing diazo materials designed to prevent duplication of images therein by contact copying with actinic light.
Micropublishing uses microforms (films, fiche, etc.) for distribution of published material. These films often contain original works unavailable in other media. While these films offer many advantages over conventional printed paper, they suffer from ease of duplication. Unauthorized copies can readily be made which would deprive the micropublisher and author from exclusive rights to such material. These copies can be made on inexpensive contact duplication equipment by relatively unskilled personnel. This invention would prevent such unauthorized duplication.
The above-noted contact duplication process requires an appreciable difference in actinic light absorption between imaged and non-imaged areas on the film. The actinic light of most importance for duplication is the near ultra-violet and blue regions of the spectrum. Thus, a measure of the difference of ultraviolet light opacity between imaged and non-imaged areas is a good indication of the ease of duplication. To prevent copying this opacity difference should approach zero. This state is difficult to obtain since most images contain an appreciable amount of ultraviolet opacity.
2. Description of the Prior Art
Several methods have previously been proposed to equalize the ultraviolet light opacity between imaged and non-imaged areas. In one, an ultraviolet light absorber or yellow dye is incorporated in the light sensitive layer of the film. This method reduces the photographic sensitivity with the result being an extremely slow film. The UV absorber may be placed in the filmbase, however, this would require a special and more expensive base. The use of multilayered coatings is another method. These coatings may contain a UV absorber or may be a surface laminate designed to blur the image on copying. Multilayer coatings are a manufacturing disadvantage since they involve higher cost and increased opportunity for film defects. The present invention is superior to these prior methods in that a single layer coating of high photographic speed on ordinary filmbase is used to produce a duplication proof film.